[FEAT] Streak freeze — allow users to protect a streak day

[Priyanshu-byte-coder]

Summary

GitHub/Duolingo-style streak freeze: let users protect their streak for one day (e.g. weekends, sick days) without breaking it.

What to build

• New Supabase table: streak_freezes(id, user_id, freeze_date, used_at)
• New API:
  • POST /api/streak/freeze — inserts a freeze for today; user can only hold 1 unused freeze at a time
  • GET /api/streak/freeze — returns whether user has a freeze available
• Update GET /api/metrics/streak to treat a freeze date as an "active day" when computing streak
• Update StreakTracker.tsx:
  • Show "Freeze available" or "No freeze" status
  • Button to "Use freeze" (calls POST /api/streak/freeze)

Supabase migration needed

CREATE TABLE streak_freezes (
  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id uuid REFERENCES users(id),
  freeze_date date NOT NULL,
  used_at timestamptz
);

Acceptance criteria

• Migration file in supabase/migrations/
• POST and GET endpoints working
• Streak API respects freeze dates
• StreakTracker shows freeze status and button

Difficulty

Advanced — requires DB, multiple API changes, and component update.

[IshitaSingh0822]

Hii @Priyanshu-byte-coder
I would like to work on this issue under GSSoC.
I have already analyzed the root cause and have a fix ready.
/assign